Which of the following is NOT a safety control used in an induced draft system?

In an induced draft system, safety controls are essential for ensuring safe and efficient operation. The correct answer is that a thermostat is not considered a safety control in this context.

A thermostat's primary function is to control the temperature within a space by regulating heating or cooling systems based on the set temperature. While it plays a crucial role in the overall operation of HVAC systems, it is not specifically designed to address safety concerns related to the draft system. Safety controls, on the other hand, are specifically engineered to monitor and mitigate potential hazards.

The pressure switch is designed to monitor the airflow or pressure in the system and will deactivate the burner if the pressure fluctuates beyond safe levels. The high limit switch serves to turn off the heating element if the temperature exceeds a pre-set limit, preventing overheating. The roll-out switch is used to detect if flames are rolling out of the combustion chamber; following its activation, it also turns off the burner to prevent dangerous situations.

Each of these safety controls actively contributes to the safe operation of an induced draft system by preventing unsafe conditions, whereas the thermostat's primary function is to manage temperature without directly addressing these safety concerns.